Brake positioning system

ABSTRACT

A saw is disclosed having a detection system adapted to detect a dangerous condition between a person and a saw blade, and a brake adapted to stop the saw blade in response to detection of the dangerous condition. The saw further includes a brake positioning system that allows the brake to be positioned in at least two different operable positions to accommodate at least two different blade diameters. The saw may include a system to detect brake-to-blade spacing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/061,162, filed Feb. 18, 2005, issuing as U.S. Pat. No. 7,228,772 onJun. 12, 2007, which was a continuation of U.S. patent application Ser.No. 09/929,244, filed Aug. 13, 2001, issuing as U.S. Pat. No. 6,857,345on Feb. 22, 2005, which claims the benefit of and priority from thefollowing U.S. Provisional Patent Applications: Ser. No. 60/225,056,filed Aug. 14, 2000, Ser. No. 60/225,057, filed Aug. 14, 2000, Ser. No.60/225,058, filed Aug. 14, 2000, Ser. No. 60/225,059, filed Aug. 14,2000, Ser. No. 60/225,089, filed Aug. 14, 2000, Ser. No. 60/225,094,filed Aug. 14, 2000, Ser. No. 60/225,169, filed Aug. 14, 2000, Ser. No.60/225,170, filed Aug. 14, 2000, Ser. No. 60/225,200, filed Aug. 14,2000, Ser. No. 60/225,201, filed Aug. 14, 2000, Ser. No. 60/225,206,filed Aug. 14, 2000, Ser. No. 60/225,210, filed Aug. 14, 2000, Ser. No.60/225,211, filed Aug. 14, 2000, and Ser. No. 60/225,212, filed Aug. 14,2000. All of these patents and applications are incorporated byreference in their entireties.

FIELD

The present invention relates to safety braking systems and moreparticularly to a brake positioning system for use in a fast actingsafety brake system.

BACKGROUND

Various active safety systems have been developed to prevent injury to auser if they approach or come into contact with a dangerous portion of amachine. Such systems typically include two components: a detectionportion and a braking portion. U.S. Pat. Nos. 3,785,230 and 4,026,177 toLokey describe one such system. The system of Lokey uses a detectionsystem that detects dangerous proximity of a part of a user's body. Thesystem relies on a radio-frequency proximity detection. When thedetection system detects a dangerous condition, a solenoid is triggeredto shift a brake into engagement with the blade. Because the system ofLokey does not wait for contact to occur, the relatively low brakeactuation speed provided by a direct-acting solenoid may be adequate toprevent injury. However, in a system that relies on contact detection,the braking time must be minimized. Even in proximity-based systems, itis beneficial to reduce braking time to minimize the chance of injury.

In a system that utilizes a brake to stop the machine, the spacingbetween the brake and the portion of the machine to be braked—typicallya cutter or saw blade—can lead to significant delays in brake action.For instance, a solenoid may supply a few pounds of force over an eighthof an inch. With a relatively light brake of 150 g, a solenoid capableof generating 10 pounds of force takes five milliseconds to move thebrake an eighth of an inch. Thus, it is important that the brake belocated as close as possible to the portion of the machine to bestopped. However, where the brake contacts the blade directly, theposition of the brake may need to be adjustable to accommodatevariations in blade size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a machine with a fast-actingsafety system according to the present invention.

FIG. 2 is a schematic diagram of an exemplary safety system in thecontext of a machine having a circular blade.

FIG. 3 is a side elevation view of a brake positioning system.

FIG. 4 is a side elevation view of an adjustable brake positioningsystem.

FIG. 5 is cross-sectional view of a portion of the brake positioningsystem of FIG. 4, taken along line 5-5.

FIG. 6 is a cross-sectional view of a portion of the brake positioningsystem of FIG. 4, taken along line 6-6.

FIG. 7 is a circuit diagram of a blade-to-pawl spacing measurementsystem.

FIG. 8 is a side elevation view of an alternative brake positioningsystem.

FIG. 9 is an isometric view of an alternative brake positioning system.

FIG. 10 is an isometric view of an exemplary pawl adapted for measuringpawl-to-blade spacing.

DETAILED DESCRIPTION

A machine that may incorporate a brake positioning system according tothe present invention is shown schematically in FIG. 1 and indicatedgenerally at 10. Machine 10 may be any of a variety of differentmachines adapted for cutting workpieces, such as wood, including a tablesaw, miter saw (chop saw), radial arm saw, circular saw, band saw,jointer, planer, etc. Machine 10 includes an operative structure 12having a cutting tool 14 and a motor assembly 16 adapted to drive thecutting tool. Machine 10 also includes a safety system 18 configured tominimize the potential of a serious injury to a person using machine 10.Safety system 18 is adapted to detect the occurrence of one or moredangerous conditions during use of machine 10. If such a dangerouscondition is detected, safety system 18 is adapted to engage operativestructure 12 to limit any injury to the user caused by the dangerouscondition.

Machine 10 also includes a suitable power source 20 to provide power tooperative structure 12 and safety system 18. Power source 20 may be anexternal power source such as line current, or an internal power sourcesuch as a battery. Alternatively, power source 20 may include acombination of both external and internal power sources. Furthermore,power source 20 may include two or more separate power sources, eachadapted to power different portions of machine 10.

It will be appreciated that operative structure 12 may take any one ofmany different forms, depending on the type of machine 10. For example,operative structure 12 may include a stationary housing configured tosupport motor assembly 16 in driving engagement with cutting tool 14.Alternatively, operative structure 12 may include a movable structureconfigured to carry cutting tool 14 between multiple operatingpositions. As a further alternative, operative structure 12 may includeone or more transport mechanisms adapted to convey a workpiece towardand/or away from cutting tool 14.

Motor assembly 16 includes one or more motors adapted to drive cuttingtool 14. The motors may be either directly or indirectly coupled to thecutting tool, and may also be adapted to drive workpiece transportmechanisms. Cutting tool 14 typically includes one or more blades orother suitable cutting implements that are adapted to cut or removeportions from the workpieces. The particular form of cutting tool 14will vary depending upon the various embodiments of machine 10. Forexample, in table saws, miter saws, circular saws and radial arm saws,cutting tool 14 will typically include one or more circular rotatingblades having a plurality of teeth disposed along the perimetrical edgeof the blade. For a jointer or planer, the cutting tool typicallyincludes a plurality of radially spaced-apart blades. For a band saw,the cutting tool includes an elongate, circuitous tooth-edged band.

Safety system 18 includes a detection subsystem 22, a reaction subsystem24 and a control subsystem 26. Control subsystem 26 may be adapted toreceive inputs from a variety of sources including detection subsystem22, reaction subsystem 24, operative structure 12 and motor assembly 16.The control subsystem may also include one or more sensors adapted tomonitor selected parameters of machine 10. In addition, controlsubsystem 26 typically includes one or more instruments operable by auser to control the machine. The control subsystem is configured tocontrol machine 10 in response to the inputs it receives.

Detection subsystem 22 is configured to detect one or more dangerous, ortriggering, conditions during use of machine 10. For example, thedetection subsystem may be configured to detect that a portion of theuser's body is dangerously close to, or in contact with, a portion ofcutting tool 14. As another example, the detection subsystem may beconfigured to detect the rapid movement of a workpiece due to kickbackby the cutting tool, as is described in U.S. Provisional PatentApplication Ser. No. 60/182,866, the disclosure of which is hereinincorporated by reference. In some embodiments, detection subsystem 22may inform control subsystem 26 of the dangerous condition, which thenactivates reaction subsystem 24. In other embodiments, the detectionsubsystem may be adapted to activate the reaction subsystem directly.

Once activated in response to a dangerous condition, reaction subsystem24 is configured to engage operative structure 12 quickly to preventserious injury to the user. It will be appreciated that the particularaction to be taken by reaction subsystem 24 will vary depending on thetype of machine 10 and/or the dangerous condition that is detected. Forexample, reaction subsystem 24 may be configured to do one or more ofthe following: stop the movement of cutting tool 14, disconnect motorassembly 16 from power source 20, place a barrier between the cuttingtool and the user, or retract the cutting tool from its operatingposition, etc. The reaction subsystem may be configured to take acombination of steps to protect the user from serious injury. Placementof a barrier between the cutting tool and teeth is described in moredetail in U.S. Provisional Patent Application Ser. No. 60/225,206,entitled “Cutting Tool Safety System,” filed Aug. 14, 2000 by SD3, LLC,the disclosure of which is herein incorporated by reference. Retractionof the cutting tool from its operating position is described in moredetail in U.S. Provisional Patent Application Ser. No. 60/225,089,entitled “Retraction System For Use In Power Equipment,” filed Aug. 14,2000 by SD3, LLC, the disclosure of which is herein incorporated byreference.

The configuration of reaction subsystem 24 typically will vary dependingon which action(s) are taken. In the exemplary embodiment depicted inFIG. 1, reaction subsystem 24 is configured to stop the movement ofcutting tool 14 and includes a brake mechanism 28, a biasing mechanism30, a restraining mechanism 32, and a release mechanism 34. Brakemechanism 28 is adapted to engage operative structure 12 under theurging of biasing mechanism 30. During normal operation of machine 10,restraining mechanism 32 holds the brake mechanism out of engagementwith the operative structure. However, upon receipt of an activationsignal by reaction subsystem 24, the brake mechanism is released fromthe restraining mechanism by release mechanism 34, whereupon, the brakemechanism quickly engages at least a portion of the operative structureto bring the cutting tool to a stop.

It will be appreciated by those of skill in the art that the exemplaryembodiment depicted in FIG. 1 and described above may be implemented ina variety of ways depending on the type and configuration of operativestructure 12. Turning attention to FIG. 2, one example of the manypossible implementations of safety system 18 is shown. System 18 isconfigured to engage an operative structure having a cutting tool in theform of a circular blade 40 mounted on a rotating shaft or arbor 42.Blade 40 includes a plurality of cutting teeth (not shown) disposedaround the outer edge of the blade. As described in more detail below,braking mechanism 28 is adapted to engage the teeth of blade 40 and stopthe rotation of the blade. U.S. Provisional Patent Application Ser. No.60/225,210, entitled “Translation Stop For Use In Power Equipment,”filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is hereinincorporated by reference, describes other systems for stopping themovement of the cutting tool. U.S. Provisional Patent Application Ser.No. 60/225,058, entitled “Table Saw With Improved Safety System,” filedAug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser.No. 60/225,057, entitled “Miter Saw With Improved Safety System,” filedAug. 14, 2000 by SD3, LLC, the disclosures of which are hereinincorporated by reference, describe safety system 18 in the context ofparticular types of machines 10.

In the exemplary implementation, detection subsystem 22 is adapted todetect the dangerous condition of the user coming into contact withblade 40. The detection subsystem includes a sensor assembly, such ascontact detection plates 44 and 46, capacitively coupled to blade 40 todetect any contact between the user's body and the blade. Typically, theblade, or some larger portion of cutting tool 14 is electricallyisolated from the remainder of machine 10. Alternatively, detectionsubsystem 22 may include a different sensor assembly configured todetect contact in other ways, such as optically, resistively, etc. Inany event, the detection subsystem is adapted to transmit a signal tocontrol subsystem 26 when contact between the user and the blade isdetected. Various exemplary embodiments and implementations of detectionsubsystem 22 are described in more detail in U.S. Provisional PatentApplication Ser. No. 60/225,200, entitled “Contact Detection System ForPower Equipment,” filed Aug. 14, 2000 by SD3, LLC, and U.S. ProvisionalPatent Application Ser. No. 60/225,211, entitled “Apparatus And MethodFor Detecting Dangerous Conditions In Power Equipment,” filed Aug. 14,2000 by SD3, LLC, the disclosures of which are herein incorporated byreference.

Control subsystem 26 includes one or more instruments 48 that areoperable by a user to control the motion of blade 40. Instruments 48 mayinclude start/stop switches, speed controls, direction controls, etc.Control subsystem 26 also includes a logic controller 50 connected toreceive the user's inputs via instruments 48. Logic controller 50 isalso connected to receive a contact detection signal from detectionsubsystem 22. Further, the logic controller may be configured to receiveinputs from other sources (not shown) such as blade motion sensors,workpiece sensors, etc. In any event, the logic controller is configuredto control operative structure 12 in response to the user's inputsthrough instruments 48. However, upon receipt of a contact detectionsignal from detection subsystem 22, the logic controller overrides thecontrol inputs from the user and activates reaction subsystem 24 to stopthe motion of the blade. Various exemplary embodiments andimplementations of control subsystem 26 are described in more detail inU.S. Provisional Patent Application Ser. No. 60/225,059, entitled “LogicControl For Fast Acting Safety System,” filed Aug. 14, 2000 by SD3, LLC,and U.S. Provisional Patent Application Ser. No. 60/225,094, entitled“Motion Detecting System For Use In Safety System For Power Equipment,”filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are hereinincorporated by reference.

In the exemplary implementation, brake mechanism 28 includes a pawl 60mounted adjacent the edge of blade 40 and selectively moveable to engageand grip the teeth of the blade. Pawl 60 may be constructed of anysuitable material adapted to engage and stop the blade. As one example,the pawl may be constructed of a relatively high strength thermoplasticmaterial such as polycarbonate, ultrahigh molecular weight polyethylene(UHMW) or Acrylonitrile Butadiene Styrene (ABS), etc., or a metal suchas aluminum, etc. It will be appreciated that the construction of pawl60 will vary depending on the configuration of blade 40. In any event,the pawl is urged into the blade by a biasing mechanism in the form of aspring 66. In the illustrative embodiment shown in FIG. 2, pawl 60 ispivoted into the teeth of blade 40. It should be understood that slidingor rotary movement of pawl 60 might also be used. The spring is adaptedto urge pawl 60 into the teeth of the blade with sufficient force togrip the blade and quickly bring it to a stop.

The pawl is held away from the edge of the blade by a restrainingmechanism in the form of a fusible member 70. The fusible member isconstructed of a suitable material adapted to restrain the pawl againstthe bias of spring 66, and also adapted to melt under a determinedelectrical current density. Examples of suitable materials for fusiblemember 70 include NiChrome wire, stainless steel wire, etc. The fusiblemember is connected between the pawl and a contact mount 72. Preferably,fusible member 70 holds the pawl relatively close to the edge of theblade to reduce the distance the pawl must travel to engage the blade.Positioning the pawl relatively close to the edge of the blade reducesthe time required for the pawl to engage and stop the blade. Typically,the pawl is held approximately 1/32-inch to ¼-inch from the edge of theblade by fusible member 70, however other pawl-to-blade spacings mayalso be used within the scope of the invention.

Pawl 60 is released from its unactuated, or cocked, position to engageblade 40 by a release mechanism in the form of a firing subsystem 76.The firing subsystem is coupled to contact mount 72, and is configuredto melt fusible member 70 by passing a surge of electrical currentthrough the fusible member. Firing subsystem 76 is coupled to logiccontroller 50 and activated by a signal from the logic controller. Whenthe logic controller receives a contact detection signal from detectionsubsystem 22, the logic controller sends an activation signal to firingsubsystem 76, which melts fusible member 70, thereby releasing the pawlto stop the blade. Various exemplary embodiments and implementations ofreaction subsystem 24 are described in more detail in U.S. ProvisionalPatent Application Ser. No. 60/225,056, entitled “Firing Subsystem ForUse In Fast Acting Safety System,” filed Aug. 14, 2000 by SD3, LLC, U.S.Provisional Patent Application Ser. No. 60/225,170, entitled“Spring-Biased Brake Mechanism for Power Equipment,” filed Aug. 14, 2000by SD3, LLC, and U.S. Provisional Patent Application Ser. No.60/225,169, entitled “Brake Mechanism For Power Equipment,” filed Aug.14, 2000 by SD3, LLC, the disclosures of which are herein incorporatedby reference.

It will be appreciated that activation of the brake mechanism willrequire the replacement of one or more portions of safety system 18. Forexample, pawl 60 and fusible member 70 typically must be replaced beforethe safety system is ready to be used again. Thus, it may be desirableto construct one or more portions of safety system 18 in a cartridgethat can be easily replaced. For example, in the exemplaryimplementation depicted in FIG. 2, safety system 18 includes areplaceable cartridge 80 having a housing 82. Pawl 60, spring 66,fusible member 70 and contact mount 72 are all mounted within housing82. Alternatively, other portions of safety system 18 may be mountedwithin the housing. In any event, after the reaction system has beenactivated, the safety system can be reset by replacing cartridge 80. Theportions of safety system 18 not mounted within the cartridge may bereplaced separately or reused as appropriate. Various exemplaryembodiments and implementations of a safety system using a replaceablecartridge are described in more detail in U.S. Provisional PatentApplication Ser. No. 60/225,201, entitled “Replaceable Brake MechanismFor Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosure ofwhich is herein incorporated by reference.

While one particular implementation of safety system 18 has beendescribed, it will be appreciated that many variations and modificationsare possible within the scope of the invention. Many such variations andmodifications are described in U.S. Provisional Patent Application Ser.Nos. 60/182,866 and 60/157,340, the disclosures of which are hereinincorporated by reference.

A brake positioning system according to the present invention is showngenerally at 800 in FIG. 3. Cartridge 80 and brake pawl 60 are typicallypivotally mounted on a large pin 802. The cartridge and pawl are fixedtogether until the brake is fired, at which time the brake pawl isshoved rapidly into the blade. The motion of the blade and geometry ofthe pawl then cause the blade to drive deeply into the pawl creatingtremendous deceleration. Pin 802 is sufficiently large, typically 0.75inches, to absorb the impact of deceleration without damage. The largediameter of pin 802 also reduces the chance that it will fracture brakepawl 60 during braking. The pivotal mounting of the cartridge on the pinpermits the spacing between the blade and the face of the brake pawl tobe adjusted by rotating the cartridge around the pin. The brake positionsystem serves to establish and maintain the proper spacing between theface of the pawl and the perimeter of blade 40.

In its simplest form, brake positioning system 800 incorporates a fixedpin 804 to position cartridge 80, and thereby brake pawl 60. Thisarrangement is generally sufficient where the size of the blade is knownand sufficiently fixed for all blades that might be used. Pin 804 isarranged parallel to pin 802 to allow cartridge 80 to be slid onto bothpins simultaneously. A flexible snap clip 806 snaps over the edge ofcartridge 80 to retain it on the pins. When the cartridge is to beremoved, the clip is lifted away from the cartridge, and the cartridgeis slipped off of the pins. A clearance pin 808 is preferably mounted ata fixed radius from the arbor axis, 5 1/16^(th) inches for instance, toinsure that no larger blade than will clear the pawl will fit on thesaw. The clearance pin is preferably located at a just slightly smallerradial position from the arbor than the nearest portion of the pawl sothat the blade will contact the pin prior to contacting the pawl.Alternatively, the pin may take the form of a curved arc that issufficiently large to insure that at least one tooth of the blade willengage it.

An adjustable brake positioning system 800 is shown in FIGS. 4-6. Brakepositioning system 800 includes a plurality of positioning teeth 812formed on the back of cartridge 80. A corresponding plurality ofpositioning teeth 814 are formed on a cartridge mounting surface 816.The teeth preferably have a pitch of approximately 1/32nd to ¼^(th) ofan inch. The teeth are spaced so that relatively small adjustments canbe made by selecting where to engage the teeth. A curved wall 818 isformed along part of the inside front edge of the cartridge. The curvedwall 818 is positioned to engage the perimeter of the blade just priorto the positioning teeth engaging each other as the cartridge is slippedonto pin 802. This insures that the pawl will be spaced back from theblade by at least the distance the wall projects forward from thepawl—typically 1/16^(th) to ⅛^(th) inch. Once the positioning teeth areengaged, the rotational position of the cartridge is fixed. Thecartridge is then slid the rest of the way onto the pin. Snap clip 806retains the cartridge against mounting surface and in proper position. Atab 820 formed on the edge of the cartridge extends over the blade. Thetab blocks the blade from being removed unless the cartridge ispartially disengaged and rotated back away from the blade. Thus, the tabinsures that the blade cannot be removed and replaced with a new bladewithout resetting the position of the cartridge. It can be seen that bymaking the cartridge pivotal on pin 802, adjustable positioning of thebrake pawl relative to the blade is simplified.

Because of the importance of establishing correct pawl-to-blade spacing,it may be desirable to incorporate a spacing detection system to insurecorrect spacing. One example of such a system is shown at 824 in FIG. 7.System 824 includes an electrode 826 located on the face of the pawladjacent the blade. As described in U.S. Provisional Patent ApplicationSer. No. 60/225,200, titled “Contact Detection System for PowerEquipment,” and U.S. Provisional Patent Application Ser. No. 60/225,211,titled “Apparatus and Method for Detecting Dangerous Conditions in PowerEquipment,” both filed Aug. 14, 2000, in one contact detection systemsuitable for use with the present invention, an electrical signal isapplied to the blade via a drive electrode. This signal can be picked upby electrode 826 and monitored to ensure that it has an amplitude in apredetermined range. In particular, the amplitude detected by electrode826 will fall off rapidly with distance from the blade. Therefore, bymonitoring the detected amplitude, proper spacing can be verified. Thesystem preferably deactivates or prevents initial actuation of themachine if the detected spacing is outside normal range. The user isthen signaled to make appropriate adjustment. Electrode 826 may takemany forms, including capacitive plates, optical sensors, magneticsensors, etc.

An alternative brake positioning system 800 is shown in FIG. 8. Theposition system of FIG. 8 utilizes a snap catch 830 with a rib 832facing the cartridge. The catch is mounted to cartridge support surface816 and is biased to push against the cartridge. The end face of thecartridge includes a groove 834 adapted to receive rib 832. In use, thecartridge is slipped over pin 802 while rotated back from the blade.Once the cartridge is fully installed on the pin, it is rotated forwarduntil rib 832 snaps into groove 834. A small ledge 836 projects over theedge of cartridge 80 when the rib is engaged in the groove to preventthe cartridge from vibrating off along the axis of the pin. Once thecartridge is fired, the user can lift tab 838 to disengage the rib andallow the cartridge to rotate back. The backward rotation can be used torelease any remaining pressure from the actuation spring, if any, in thecartridge.

FIG. 9 shows another brake positioning system 800. In the system of FIG.9, cartridge 80 includes a recess 850 formed on one side. A spring latch852 is positioned to engage recess 850 as cartridge 80 is rotated backaway from the blade. The latch is positioned to locate the face of thepawl approximately ⅛^(th) of an inch away from the perimeter of theblade, although different spacing could of course be used. The user canremove the cartridge by lifting the latch, rotating the cartridgeforward until it clears the latch and then sliding the cartridge off pin802. As described in more detail in U.S. Provisional Patent ApplicationSer. No. 60/225,201, titled “Replaceable Brake Mechanism for PowerEquipment,” filed Aug. 14, 2000, when the cartridge is fired, the pawlwill normally be somewhat embedded on the blade and biased toward theblade by a spring 66. A release pin 756 is removable to release the backof the spring and remove the biasing pressure. This allows the pawl tobe loosened from the blade more easily and eliminates the pressure onthe blade that would otherwise make removal of the blade more difficult.

Logic controller 50 may also be configured to monitor the pawl-to-bladespacing. Many cutting tools such as saw blades do not have preciselyuniform dimensions. As a result, when a new blade is installed on a saw,for example, the pawl may no longer be correctly spaced from the blade.An incorrectly positioned pawl may slow the stopping speed of the pawlor prevent the pawl from stopping the blade. Therefore, to ensure theblade is stopped with uniform braking speed, it may be necessary toadjust the position of the pawl whenever a blade is replaced.Configuring logic controller 50 to detect incorrect blade-to-pawlspacing, as described above and as described in U.S. Provisional PatentApplication Ser. No. 60/225,059, entitled “Logic Control For Fast ActingSafety System,” provides an additional level of assurance that a user isprotected against accidental contact with the blade.

It will be appreciated that there are many ways in which incorrectspacing between blade 40 and pawl 60 may be detected. One such way isdescribed above in connection with FIGS. 5 and 7. As another example,FIG. 10 illustrates a pawl 945 having a capacitive system for detectingcorrect pawl spacing. Similar to pawl 40 shown in FIG. 2, pawl 945 mayinclude a portion 946 that is beveled or otherwise shaped to quickly andcompletely engage the teeth of a cutting tool. In addition, pawl 945includes a pair of generally parallel, spaced-apart arms 947 whichextend beyond portion 946. Arms 947 are disposed to extend on eitherside of the blade, without touching the blade, when the pawl is in placeadjacent the blade. Each arm includes a capacitor plate electrode 826disposed on the inside surface of the arm adjacent the blade. Conductiveleads 949 run from each plate 826 to suitable blade detector circuitry.

Capacitor plates 826 are positioned on arms 947 such that, when the pawlspacing is within a desired range, the blade extends between the twocapacitor plates. It will be appreciated that the capacitance acrossplates 826 will vary depending on whether the blade is positionedbetween the sensors. The blade detector circuitry is configured to drivean electrical signal through conductive leads 949 and to detect changesin the capacitance across the plates. Suitable circuitry that may beused with pawl 945 is well known to those of skill in the art. Oneexemplary pawl-to-blade spacing detection circuit was discussed aboveand is shown in FIG. 7. An electrical signal applied to the blade can bepicked up by either or both of plates 826 and monitored to insure thatthe signal has an amplitude in a predetermined range. By monitoring thedetected amplitude, proper spacing can be verified. If the proper signalis not detected, a circuit, such as circuit 824 in FIG. 7, conveys anerror signal to logic controller 50, which prevents operation of machine10 until proper pawl-to-blade spacing is detected. Other examplesinclude circuits similar to the exemplary contact detection circuitsdescribed in U.S. Provisional Application Ser. No. 60/225,200 entitled“Contact Detection System for Power Equipment.”

Capacitor plates 826 can optionally be shaped to detect when the pawl istoo close to the blade as well as not close enough. Alternatively, twopairs of capacitor plates may be positioned on the pawl: one pair todetect if the pawl is too close to the blade, and the other pair todetect if the pawl is too far from the blade. In any event, the detectorcircuitry is configured to transmit an error signal to logic controller50, which then takes appropriate action.

While exemplary automatic pawl spacing detection systems have beendescribed above, it will be appreciated that there are many possiblevariations within the scope of the invention. For example, bothcapacitor plates may be positioned on the same side of the blade ratherthan on opposite sides. The plates and/or blade detection circuitry maybe separate from the pawl. In the latter case, for example, the platesand detection circuitry may be mounted on a separate electronics boardassociated with the pawl. Alternatively, the plates may be replaced withone or more light-emitting diodes and detectors such that, when the pawlis properly positioned, the blade obstructs the optical path between thediodes and detectors. Other methods of detecting the proximity of theblade to the pawl are also possible. As a further option, plates 826 mayfunction as charge plates 44, 46 as well as pawl-spacing detectors. Inaddition, a plate may be mounted on beveled face of a pawl, such as onface 946 of the pawl shown in FIG. 10. This plate can be used to detectthe drive input signal used for contact detection. The amplitude of thesignal detected at the plate will be inversely proportional to the spacebetween the sensor and the teeth of the blade. If this signal does nothave an amplitude over a given threshold, the system would interpretthis as indicating that the pawl face is not close enough to the blade.

In embodiments where portions of safety system 18 are mounted in areplaceable cartridge 80, the correct blade-to-pawl spacing may bedetected by measuring the blade-to-cartridge spacing. For example,capacitor plates 826 may be placed on cartridge housing 82 rather thanon a pawl itself.

INDUSTRIAL APPLICABILITY

The present invention is applicable to power equipment, and specificallyto woodworking equipment such as table saws, miter saws, band saws,circular saws, jointers, etc.

It is believed that the disclosure set forth above encompasses multipledistinct inventions with independent utility. While each of theseinventions has been disclosed in its preferred form, the specificembodiments thereof as disclosed and illustrated herein are not to beconsidered in a limiting sense as numerous variations are possible. Thesubject matter of the inventions includes all novel and non-obviouscombinations and subcombinations of the various elements, features,functions and/or properties disclosed herein. No single feature,function, element or property of the disclosed embodiments is essentialto all of the disclosed inventions. Similarly, where the claims recite“a” or “a first” element or the equivalent thereof, such claims shouldbe understood to include incorporation of one or more such elements,neither requiring nor excluding two or more such elements.

It is believed that the following claims particularly point out certaincombinations and subcombinations that are directed to one of thedisclosed inventions and are novel and non-obvious. Inventions embodiedin other combinations and subcombinations of features, functions,elements and/or properties may be claimed through amendment of thepresent claims or presentation of new claims in this or a relatedapplication. Such amended or new claims, whether they are directed to adifferent invention or directed to the same invention, whetherdifferent, broader, narrower or equal in scope to the original claims,are also regarded as included within the subject matter of theinventions of the present disclosure.

1. A woodworking machine comprising: a blade; a detection system adaptedto detect a dangerous condition between a person and the blade; amounting pin; a brake supported by the mounting pin, where the brake isadapted to decelerate the blade in response to detection of thedangerous condition; and a brake positioning system configured to pivotthe brake on the mounting pin to selectively position the brake relativeto the blade without activating the brake to decelerate the blade; wherethe blade is planar and where the brake positioning system is configuredto pivot the brake around an axis perpendicular to the plane of theblade.
 2. The woodworking machine of claim 1, where the dangerouscondition is contact between a person and the blade.
 3. The woodworkingmachine of claim 1, where the dangerous condition is proximity between aperson and the blade.
 4. The woodworking machine of claim 1, where themachine is a table saw.
 5. The woodworking machine of claim 1, where theblade is a circular blade with a cutting edge at its perimeter.
 6. Thewoodworking machine of claim 5, where the mounting pin is positionedbeyond the cutting edge of the blade.
 7. The woodworking machine ofclaim 1, where the blade has a cutting edge, and where the brakepositioning system is configured to pivot the brake toward and away fromthe cutting edge.